EP0235215A1 - Ecran de retroprojection transparent - Google Patents

Ecran de retroprojection transparent

Info

Publication number
EP0235215A1
EP0235215A1 EP86905242A EP86905242A EP0235215A1 EP 0235215 A1 EP0235215 A1 EP 0235215A1 EP 86905242 A EP86905242 A EP 86905242A EP 86905242 A EP86905242 A EP 86905242A EP 0235215 A1 EP0235215 A1 EP 0235215A1
Authority
EP
European Patent Office
Prior art keywords
screen
approx
lenses
lens
strip
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP86905242A
Other languages
German (de)
English (en)
Inventor
Erik Clausen
Johannes Clausen
Holger Jensen
Finnur Sturluson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
SCAN SCREEN AS
Original Assignee
SCAN SCREEN AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by SCAN SCREEN AS filed Critical SCAN SCREEN AS
Publication of EP0235215A1 publication Critical patent/EP0235215A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00—Projectors or projection-type viewers; Accessories therefor
    • G03B21/54—Accessories
    • G03B21/56—Projection screens
    • G03B21/60—Projection screens characterised by the nature of the surface
    • G03B21/62—Translucent screens
    • G03B21/625—Lenticular translucent screens

Definitions

  • the present invention relates to a transparent . rear projec ⁇ tion screen of the kind comprising a sheet-shaped Fresnel lens and a picture-forming sheet-shaped screen mounted in front of the Fresnel lens (as viewed by the watcher or watchers) .
  • the back of the screen has vertical , backward convex lenses which are situated vertically in the working position of the screen , and vertical masking strips on its front which are interspaced by strip-shaped sections positioned opposite to the backward convex lenses, each of these last-mentioned lenses being designed in such a way as to refract the light rays from the Fresnel lens which hit them so that these rays are emitted through the strip-shaped sections .
  • Such a screen has the effect that the backward convex lenses of the picture-forming screen focus all the rays coming from the Fresnel lens on the strip-shaped sections so that loss of light is avoided and a strongly luminous picture is thus obtained .
  • the mask ⁇ ing strips provide the screen with a good contrast effect since to a great extent they prevent ingress of disturbing light from the front into the picture-forming screen .
  • I n order to reduce this pitch it is necessary that the lenses facing backward are designed with a correspondingly reduced focal length since if not they will be unable to focus all the light on the strip-shaped sections .
  • a screen of the kind referred to above is characteristic in that every two of the backward convex lenses on the back of the picture-forming screen are separa ⁇ ted by a vertical intermediate lens having two opposite sides designed in such a way that the light rays from the Fresnel lens entering one side of each intermediate lens, are refracted so that they flow gene- rally in the direction of the strip-shaped section which is positioned opposite to the backward convex lens adjacent to the other side of the intermediate lens concerned , and that the light rays coming from the Fresnel lens and entering the other side of the intermediate lens concerned are refracted so that they flow general ly in the direction of the strip-shaped section which is positioned opposite of the back ⁇ ward convex lens adjacent to said one side of the intermediate lens concerned .
  • the strip-shaped sections can be made narrow for obtaining a good picture resolution or definition without weakening the back of the picture-forming screen since the notches which would otherwise occur between the backward convex lenses by increasing their curvature (or reducing thei r focal length ) are replaced by the intermediate lenses . Since these lenses also refract the light from the Fresnel lens which hits them so that this light is emitted through the strip-shaped sections , this light is utilized for the il lumination of the picture.
  • Rear projecting screens of the kind here concerned are especially suitable for showing of television pictures which are pro ⁇ substituted by three projectors directed towards the back of the screen and each emitting a black-white tv picture and where a filter is placed in front of each projector so that the picture transferred to the screen by one projector is red , by the second projector green , and by the third projector blue.
  • these three projectors cannot be placed so that their optical axes coincide since in that case they will. shade each other, they are placed side by side.
  • their optical axes have to be directed towards the centre of the back of the screen in order to produce as good coincidence of the three projec ⁇ ted pictures as possible, the rays hitting the back of the projection screen will converge at angles of approx . 7°.
  • a preferred embodiment of the screen according to the present invention where the strip-shaped sections between the mask ⁇ ing strips are forward convex as well as where the focal length of the backward convex lenses corresponds generally to the distance between the apices of the backward convex lenses and the apices of the forward convex sections, is according to the invention characte ⁇ ristic in that the focal length of these forward convex sections corresponds generally to the focal length of the backward convex lenses .
  • Fig . 1 is a schematic representation of a preferred use of the rear projection screen according to the invention .
  • Fig . 2 in perspective is a section of a picture-forming screen for an embodiment of the rear projection screen according to the invention
  • Fig . 3 is a section through a part of an imagined embo- diment of a rear projection screen for elucidation of the problem which the present invention aims to solve
  • Fig . 4 is part of a section through an embodiment of the rear projection screen according to the present invention
  • Fig . 5 is part of the picture-forming screen for the rear projection screen shown in Fig . 3
  • Fig . 6 and 7 are pictures for elucidation of the ray path in a picture-forming screen for the embodiment shown in Fig . 4 of the rear projection screen according to the invention
  • Fig . 8 is a section of Fig . 4 on an enlarged scale
  • Fig . 9 and 10 are further embodiments of the picture-form-
  • Fig . 1 shows three projectors 1 ,2 and 3 for projection of television pictures on the back of a projection screen 4.
  • Each projec- tor transfers a black-white television picture, but a filter is placed in front of projector 1 so that the picture which this projector trans ⁇ fers to screen 4 is red .
  • a filter is placed in front of projector 2 so that the picture which this projector transfers to screen 4 is green , and projector 3 uses a filter so that the picture transferred by this projector is blue.
  • the three projectors 1 , 2 and 3 are placed side by side, with the optical axis 7 of the central projector 2 at right angles to the centre of screen 1 .
  • the projectors Since the projectors have a certain width , they cannot be placed with their optical axes 6 and 8 coinci ⁇ ding with axis 7, and instead the three optical axes form angles of 7 two and two. It is difficult to go below these 7 because of the size of the projectors . On the contrary, the development is towards more and more powerful projectors which therefore take up more space in the lateral direction so that the said angle of 7 may very well increase up to 10° .
  • the optical axes are directed towards the centre of screen 4 and the projectors are arranged so that the pictures projected on to the back of screen 4 cover each other as well as possible.
  • Fig . 1 shows the ray path from the three projectors to the centre of screen 4 as well as the ray path from the three projectors to a point on the screen which is to the left of the centre. It will be understood from Fig . 1 that every point on the back of screen 4 will be hit by red, green and blue light rays forming the angle relative to each other which is explained in the foregoing .
  • the rear projection screen according to the present inven ⁇ tion is designed especially, but not exclusively, for the application explained in the foregoing .
  • Fig . 3 shows an imagined idealized screen . It consists of a sheet-shaped Fresnel lens 20 with its flat back facing the projector or the projectors during use, and with its front provided with concentric grooves , one side of which is at right angles to the plane of the sheet while the other side is inclined relative thereto.
  • a screen which consists of light refracting material , e. g . acrylic, is characteristic in that it deflects rays coming from behind so that these rays leave this screen parallel to each other. However, this only applies to the rays which come from a projector whose optical axis is at right angles to the screen and which pass through the centre of the concentric grooves . This will thus apply to the green rays from projector 2 in Fig . 1 .
  • a picture-forming lens 21 is places in front of the Fresnel lens . It also consists of a light refracting material e . g . acrylic . This screen is designed with backward convex lenses 22 which extend vertically in the working position of the screen .
  • the front of screen 21 is provided with a masking consisting of strips 23 consisting of black paint or inc which are applied to elevations 24, the sides 25 of which are almost at right angles to the plane of the screen .
  • Strip- shaped sections 26 are situated between every two adjacent strips . I n the embodiments shown these strip-shaped sections are designed as forward convex lenses since, as mentioned , the embodiments shown are intended primarily for use as described in connection with Fig . 1 .
  • Such forward convex sections will actually have the effect of compensating for the convergence of the optical axes 6, 7 and 8 of the projectors mentioned in the foregoing , viz. so that the red and blue rays projected from projectors 1 and 3 will be deflected so as to flow parallel to the rays coming from projector 2 when they leave the front of the composite screen .
  • screen 21 in Fig . 3 is idealized and has the following characteristics: A high masking percentage since masking strips 23 cover approximately 40% of the screen front.
  • the pitch of screen 21 is very small.
  • the pitch of the screen is understood the distance a shown in Fig . 3, i .e. the distance from centre to centre of masking strips 23. This is tantamount to the backward convex lenses 22 also having the pitch distance a between their apices.
  • the high masking percentage has the effect that little light from the outside can penetrate into the screen front and thus blur the projected picture, and the screen thus has a good contrast effect.
  • the screen also has a good picture resolution or definition capability since by virtue of a small pitch the strip-shaped sections 26 are also placed close to each other and are also narrow thanks to the large width of the masking strips .
  • Screen 21 also has the effect that the picture is well illuminated .
  • the backward convex lenses 22 are actually designed in such a way that the light hitting them from behind from the Fresnel lens is deflected so that the light is direc ⁇ ted towards the strip-shaped sections 26 so that no light is lost because of absorption in masking strips 23 or as a result of total reflection when it hits the forward surface of screen 21 . To achieve this, the backward convex lenses 22 must be strongly curved as shown in Fig .
  • distance b_. between the notches 27 formed between the backward convex lenses and the notches formed by the adjacent edge parts of the forward convex lenses 26 and the sides 25 is very short. Since the thickness of screen 21 is already very small (0.80 mm in Fig . 3) , the effect of the short distances b- or rather the deep notches 27 result in that the strength of screen 21 becomes very weak. I n the first place, the remaining material thickness b- is very small , and in the second place the notches 27 result in a mar ⁇ ked notch sensitivity .
  • Such a notch sensitivity and weakening of the picture-for- ming screen 21 is remedied according to the present invention such as explained in the following .
  • Fig . 4 shows an embodiment of the rear projection screen according to the present invention with a picture-forming screen 21 which as far as the optical characteristics are concerned corresponds to screen 21 in Fig . 3, but where the weaknesses explained in the foregoing have been remedied .
  • This is achieved by providing inter ⁇ mediate lenses 28 between every two of the backward convex lenses 22.
  • Every intermediate lenses 28 has two sides 29 and 30 which in the embodi ⁇ ments shown are designed with a curvature turning away from each other, but which may very well be plane.
  • Fig . 4 shows an embodiment of the rear projection screen according to the present invention with a picture-forming screen 21 which as far as the optical characteristics are concerned corresponds to screen 21 in Fig . 3, but where the weaknesses explained in the foregoing have been remedied .
  • This is achieved by providing inter ⁇ mediate lenses 28 between every
  • the presence of the intermediate lenses also has the effect that the vertical angle c of the backward convex lenses 22 is increa- sed greatly, being 38° in the embodiment in Fig . 3, but 56° in the embodiment in Fig . 4. This also facilitates the design of the tools for production of the backward convex lenses 22.
  • Fig . 8 shows an intermediate lens 28 on a furhter enlarged scale, from which it can be seen that sides 29 and 30 curving away from each other each has a radius of curvature of approx . 0.80 mm . It can also be seen that tangent planes 32, 33 to the side parts of lens sides 29 and 30 adjacent to the root end 28 of the intermediate lens, form a mutual angle of 50 . This angle may, however, vary within wide limits, viz. 40° to 75°, appropriately between 45 and 60° and is preferably 50° as shown . If sides 29 and 30 are plane, they will preferably form a vertical angle of 55 which may, how ⁇ ever, also vary within wide limitations, viz.
  • the embodiment shown in Fig . 8 sides 29 and 30 have a radius of curvature of 0.80 mm, but this radius may also vary within wide limits, viz. 0.2 and 2.0 mm, appropriately between 0.5 and 1 .5 mm and is preferably 0.80 mm as mentioned .
  • the ray path through the embodiments shown will now be explained further.
  • the drawing shows only the ray path from a single projector, the optical axis of which is at right angles to the screen and passes through its centre, i .e. the ray path of green light emitted by projector 2, in the case where the screen is used as explained in connection with Fig . 1 .
  • the ray paths of the red and blue lights will , as far as the flow within the screens and between these is concerned , diverge by the 7 mentioned in the foregoing relative to the green light, but this divergence will be compensated for as explained , thanks to the design of the strip-shaped sections 26 as forward convex lenses . Consequently, it will also be understood that if the screen is used in connection with a single projector, the strip-sha ⁇ ped sections 26 will be plane.
  • the ray path through the idealized screen 21 can be seen in Fig . 5 from which it appears that the parallel rays coming from behind and being at right angles to the plane of the screen are deflected so that they emit from the strip-shaped sections 26.
  • the focal length of the backward convex lenses 22 corresponds to the distance between the apices of two lenses 22, 26 opposite to each other.
  • the strip-shaped sections 26 designed as lenses have a focal length which corresponds to the focal length of the backward convex lenses 22.
  • the picture-forming screen 21 i Figs. 4,6 and 7 has a thickness of 1.0 mm. As previously mentioned, the thickness may, however, be smaller and larger such as it can be seen from Figs. 9 and 10 respectively, as Fig. 9 shows an embodiment of the picture- forming screen 21 with a thickness of 0.8 mm, and Fig. 10 shows an embodiment of the picture-forming screen 21 with a thickness of 1.2 mm. In all cases a ray path is obtained as previously explained.
  • the width of the intermediate lenses in these examples constitutes 20% of the screen pitch . Deviations may, however, also occur here since this width can deviate between 15 and 25%, appropriately between approx . 17 and 23%, and as mentio ⁇ ned preferably is approx. 20% of the pitch .

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Overhead Projectors And Projection Screens (AREA)

Abstract

Un écran de rétroprojection comporte une lentille de Fresnel (20) devant laquelle est placé un écran (21) de formation d'images. Ce dernier possède sur sa face arrière des lentilles (22) verticales convexes vers l'arrière et sur sa face frontale des bandelettes verticales (23) de masquage, et des parties (26) en forme de bande situées entre les bandelettes de masquage (23) et face aux lentilles convexes vers l'arrière (22). Chacune de celles-ci est destinée à réfracter les rayons lumineux provenant de l'arrière de manière à les diriger vers les parties (26) en forme de bande. Afin d'accroître la résolution de l'image ou la capacité de définition de l'écran et afin d'éviter la sensibilité à l'entaille entre les lentilles convexes vers l'arrière (22), une lentille intermédiaire (28) est prévue chaque fois entre deux lentilles convexes vers l'arrière successives. Chaque lentille intermédiaire (28) présente deux côtés (29, 30) façonnés de telle manière que les rayons qui frappent un côté (29) de chaque lentille intermédiaire (28a) sont réfractés de sorte qu'ils sont dirigés vers la partie en forme de bande (26a) située face à la lentille convexe vers l'arrière (22a), laquelle est adjacente à l'autre côté (30) de la lentille intermédiaire (28a) concernée et de telle manière que les rayons qui frappent l'autre côté (30) de la lentille intermédiaire (28a) concernée sont réfractés de sorte qu'ils sont dirigés vers la partie en forme de bande (26b) située face à la lentille convexe vers l'arrière (22b) qui est adjacente audit côté (29) de la lentille intermédiaire (28a) concernée.
EP86905242A 1985-08-30 1986-08-29 Ecran de retroprojection transparent Withdrawn EP0235215A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DK397585A DK156596C (da) 1985-08-30 1985-08-30 Transparent baglysprojektionsskaerm
DK3975/85 1985-08-30

Publications (1)

Publication Number Publication Date
EP0235215A1 true EP0235215A1 (fr) 1987-09-09

Family

ID=8128869

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86905242A Withdrawn EP0235215A1 (fr) 1985-08-30 1986-08-29 Ecran de retroprojection transparent

Country Status (5)

Country Link
US (1) US4636035A (fr)
EP (1) EP0235215A1 (fr)
AU (1) AU6289886A (fr)
DK (1) DK156596C (fr)
WO (1) WO1987001470A1 (fr)

Families Citing this family (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0721612B2 (ja) * 1986-07-25 1995-03-08 大日本印刷株式会社 透過型投影スクリ−ン用レンズシ−ト
NL8700135A (nl) * 1987-01-21 1988-08-16 Philips Nv Doorzichtprojektiescherm en doorzichtprojektiesysteem voorzien van een dergelijk scherm.
JP2670540B2 (ja) * 1987-02-28 1997-10-29 大日本印刷株式会社 レンチキユラーレンズスクリーン
KR920008057B1 (ko) * 1989-01-28 1992-09-22 주식회사 금성사 광역의 흡수율을 갖는 리어프로젝션 스크린
JPH03149540A (ja) * 1989-11-07 1991-06-26 Pioneer Electron Corp 背面投影式スクリーン
JPH03216635A (ja) * 1990-01-23 1991-09-24 Pioneer Electron Corp 投写スクリーン
US5146342A (en) * 1990-04-20 1992-09-08 Pioneer Electronic Corporation Rear projection television set with lenticular sheet and fresnel lens
JP2911627B2 (ja) * 1991-03-27 1999-06-23 株式会社日立製作所 大画面投写形ディスプレイ
JP3388780B2 (ja) * 1992-06-19 2003-03-24 株式会社日立製作所 背面投写型画像ディスプレイ装置
JP2734914B2 (ja) * 1992-12-14 1998-04-02 三菱電機株式会社 透過型スクリーンおよびその製造方法
GB9613802D0 (en) * 1996-07-01 1996-09-04 Nashua Corp Improvements in or relating to light diffusers
JP4103911B2 (ja) * 2005-02-02 2008-06-18 セイコーエプソン株式会社 スクリーン及び画像表示装置
US7911693B2 (en) * 2006-03-20 2011-03-22 Hewlett-Packard Development Company, L.P. Ambient light absorbing screen
US8979281B2 (en) 2010-06-21 2015-03-17 Disney Enterprises, Inc. System and method for imagination park tree projections
CN107430282B (zh) * 2015-03-12 2021-03-05 昕诺飞控股有限公司 光束整形设备和使用其的聚光灯

Family Cites Families (8)

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Publication number Priority date Publication date Assignee Title
JPS5552417Y2 (fr) * 1976-11-18 1980-12-05
US4536056A (en) * 1981-10-05 1985-08-20 Hitachi, Ltd. Rear projection apparatus
DK162413C (da) * 1982-06-10 1992-03-23 Dainippon Printing Co Ltd Bagfra belyst projektionsskaerm
US4509823A (en) * 1982-10-15 1985-04-09 Dai Nippon Insatsu Kabushiki Kaisha Rear projection screen
DK156188C (da) * 1983-05-10 1989-11-27 Scan Screen Production A S Transparent baglysprojektionsskaerm
JPS6027776B2 (ja) * 1983-05-20 1985-07-01 千代田化工建設株式会社 排水および雨水の回収方法
DK151320C (da) * 1983-10-12 1988-05-09 Scan Screen Transparent baglysprojektionsskaerm
US4548469A (en) * 1984-06-07 1985-10-22 Mitsubishi Rayon Co., Ltd. Rear projection screen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8701470A1 *

Also Published As

Publication number Publication date
AU6289886A (en) 1987-03-24
DK156596C (da) 1990-01-29
DK156596B (da) 1989-09-11
WO1987001470A1 (fr) 1987-03-12
DK397585D0 (da) 1985-08-30
US4636035A (en) 1987-01-13
DK397585A (da) 1987-03-01

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